While I've pondered the same question from time to time (because others are using and swearing by them), I've never been able to convince myself that its truly to my advantage....discounting the "looking professional" factor. I've shot without a grip for 35+ years of SLR/DSLR usage and do NOT see any compelling need for it, but readily accept that it does for others. I feel neither the need to defend my usage or correct that of others (much like my position on use of UV filters). I shoot an array of modes, ie landscape and portrait on an array of lenses, mostly a 24-105 and 100-400. I have size L or XL gloves (thus presumably large hands!) and again don't miss the "balance" or heft of a grip....but then I've never really used one for a sustained period. I suspect we're creatures of habit and if you're used to one thing OR the other...then that's what you prefer.
The reasons I never took the leap was:
1. they aren't cheap, ie money that could be invested in other gear (lens, upgraded body, etc)
2. I don't buy the value of the extra onboard battery. I carry 2-3 spares with me (depending on their age/capacity) BUT in my pack where the weight is much less tiring. Changing batteries is a non issue, ie seconds!
3. I do a lot of photography while hiking. Weight/bulk are important issues. Grips are a disadvantage in that regard.
4. I use L-brackets. The one that fits on an ungripped body is different than one that fits on a gripped. While I could "unmount" the grip, I don't want to incur the expense of a 2nd L-bracket or futz with changing it over as well.
I've seen online polls re who, how many use a gripped body and WHY (discounting the "me-too'ers"). On sites where the predominate lens usage is super telephotos, gripped bodies predominate. Otherwise, they appear to be in a minority. If it meets a REAL need, use it. If it doesn't, why would you? EVERYTHING comes at a cost....which can you better afford ($$$, weight, inconvenience, etc)?
A Rebel is a smaller bodied camera and perhaps a grip would improve its feel. Me, I'd rather upgrade to a larger body (ungripped).