Thanks for the replies, interesting to hear that I'm not the only one battling with these
I already grouped snipers, mortars and artillery, I'm okay at that as it's very useful to ensure that these units are always active (or when you want to fire at something in a hurry).
My rationale behind grouping all my units though is just to extend this same philosophy so I can keep all my units active and so I can always know what my army composition looks like.
It might be overkill as some of you say so maybe I'll scale back and not group EVERYTHING. For example I tried grouping MGs and ATGs yesterday but I didn't find it particularly useful since you need to micro these around any way.