Is the Trueplay necessary?

Not required, no. It can be helpful, or it can’t. Depends on your environment. You shouldn’t feel as you’re losing out if you can’t do it. I have quite a few rooms, I’ve done it in some, others I’d prefer not to. 

Note however (and I don’t mean to demean you!) that the Beam isn’t the best Sonos speaker for Atmos. It certainly can interpret it, but it doesn’t have upward firing speakers to maximize the experience, so you need to temper your expectations a bit. 

Yes I know but in much reviews they always says that the Beam is good enough for Atmos but I might try to borrow an iPhone and do the tuning, as an always in audio try and try to found the best results, right?

Maybe in the future I could add some Era 300 to my setup, thank you for always answer quickly :)

Good enough is a very slippery bit. Yes the Beam will decode and play Atmos BUT it can't compete with an Atmos speaker like the Arc that has drivers dedicated to additional (height) channels. Same for surrounds, the 100 can decode and play Atmos but compared to a 300 with dedicated drivers it is a bit thin. The 100s aren't bad, I use them with my Arc Ultra, but compared to properly positioned 300s they are a step down. The spouse didn't care about sound, she didn't want to clutter up her space.

Trueplay really depends on the room, some get a lot of good from it, others little to none. A few reports of it making things worse, not many. Personally I got tired of the expense and inconvenience of obtaining a compatible Apple device and disabled it on all my Sonos, I don't miss it or intended to buy/borrow an Apple devices to redo it.

Probably not necessary if all you have is the Beam 2.  You can still try it and if you don’t like the results you can turn TruePlay OFF.

Well, thank you Stanley for sharing your experience. I know I should not expect the best results from the Beam, but when compared to my Ray, there isn't a really noticeable change, especially when I pair it with two Era 100s and a Sub Mini. I will try tuning it, especially given the shape of my room (it's almost a cube, which is the worst for sound). It's possible that Trueplay will correct many things (as I did with REW, but now for all sources), so I have high hopes for it.

This how the Beam2 works vs the Arc Ultra in the simplest terms.

Arc Ultra

1. L/C/R front channels
2. Simulated L/R surround rear channels
3. Height Channels (upward firing speakers)

Beam 2

1. L/C/R front channels
2. Simulated L/R surround rear channels 

As the Beam2 lacks Height Channels you will not get the robust “bubble effect” as you would with the Arc Ultra. Also the Beam2’s smaller size is not suited for large rooms (although large is a relative term). Bottom-line is that the Atmos effect will be less engaging with the Beam2 for movies. You’ll probably have the best Atmos experience with music (spatial audio).

Only you can determine if TruePlay provides a measurable improvement in sound quality.

I know how physically the Sonos products works (hardware) but lastly I was talking about the sound in general as you said the Trueplay could make a improvement in the frequencies response, also in phases and other things. That is something I think my room need, thank you ​@AjTrek1 for your advice :)

For Dolby Atmos, I might start to opt for an Arc Ultra? or could be better two Era 300s as rears for my Beam?

No Ray and my Beams are gen 1, had an Arc and swapped for an Arc Ultra. Original surrounds were Play 1, tried 300s which sounded great but failed the spouse approval process and currently using 100s.

So, my original Beam 1 in my big, open L shaped space was pretty stressed filling it and we sit far enough away the imaging was weak. The Arc did well but we wanted the voice enhancements on the Ultra so we upgraded. In a 15x15 room the Beam 1 is adequate for talking heads TV but weak for movies. In a 10x10 room the Beam 1 is quite good but a Sub really helps movie sound. A spare Beam in a 6x10 bathroom does a great job for music.

I do a good bit of Atmos music and find I prefer a 300 Pair to the Arc Ultra for that. A few tracks have enough rear audio to make much use of the 100 surrounds, the 300 height audio is noticeable when present in the source.

I disabled the full Trueplay on everything but did the built-in version on everything that supports it. As said I'm not missing the full Trueplay enough to fuss with it.

Thank you both ​@Stanley_4 and ​@AjTrek1, so, since I often listen to music, it seems the Era 300s are better, I’ll think about them some more (as many people have said that).

Also, I’d like to know at what volume you play movies. For me (in a very very quiet place) 40 is loud, I almost need to shout to hear myself and my space is similar to yours @Stanley_4.

I also used the build-in Trueplay in my Era 100 and they do a noticeable change with subtle gains and more things, that’s why I’m having very high hopes in “full” Trueplay :)

Thank you for your advice! :)