They lump them all together, and just to be on the safe side, make them all yeharog v’al yaavor”
This is very true, and what got Odom and Chava into hot water. If you enforce a chumrah like its law, when the person finds out that its negotiable, often times they will retreat to a point beyond where your real deadline is.
Still, there are some practical “chumras” that steer you clear of halacha problems. Here’s one:
We were told, “Never drink from the (64 oz) bottle in the fridge. use a cup”
But if the rule is not in place, and my wife drinks from it in the frozen zone (v’hamaven, yovin), that means I cannot drink from it.
Same thing goes for using placemats / chargers. Not a halacha, but it keeps you on the right side of the law, and avoids drawing attention when it could easily be avoided.
So, some things are put in place to protect you (and your OJ)