Should a beginner roll with much bigger guys?

In short, there are potential benefits, particularly with respect to self defense. There are no weight classes on the street and all that.

But! As a white belt, especially going against bigger white belts and possibly strangers, I'd advise against it for now, at least not full on free rolling. Reason is that your technique is likely not sufficient to make up for the difference in size and there is a real risk of potentially serious injury, particularly spinal injuries. If you are not flexible or familiar enough with the movements, and your partner is smashing you, possibly in an ill controlled fashion, this can be very dangerous for you.

Once you have many months or a few years under your belt, then you should absolutely try rolling with much bigger people. See how much your technique can make up for. Size and strength is just another attribute, like flexibility, skillfulness, age, speed, stamina, conditioning. Technique and strategy can make up for discrepancies in these attributes but only to a point. There is a YouTube video where iirc Renner Gracie explains his view on it from a belt perspective, giving every 20lbs or 10y age difference approximately a belt level of skill needed make up for it. It's not that simple but it's not a bad rule of thumb.

I'm a bigger guy, have rolled with guys who are much smaller and that I have 40-60lbs on. Earlier on, I had people with a few years more training on me be able to consistently control me. But I also caused at least one injury to a friend and felt very bad about it. Now with more training and skill, that's less likely but it's still a danger and there is always responsibility on both sides. I have also in tournaments rolled with guys who had well over 60lbs on me, and won, and lost. I found it very interesting and helpful for my game.