No, not when it comes to handicaps. The mark is a leveller to the race (generally) on how each horse rates against each other.
If I ran against Usain Bolt, he would have to carry lets say a car in extra weight to give me a chance. Next time I run against a 12 year old and I would probably have to carry maybe a tv to try and level things out and finish equal which is what the handicapper tries to do.
So I have gone form carrying no extra weight to carrying a tv but only as the race conditions or competitors are different if you get what I mean, to make things supposedly level. This is me effectively dropping in class which is what Mythical Blue is doing from a class 3 lto to a class 5 today. (The more I look the more I like this each way.)
If Mythical Blue is rated 100, I haven't looked but say 100 and Spring Green is carrying 95 then whatever handicap race they run in Mythical Blue will carry 5lbs more, until their ratings change.
I don't go too much on the odd pound here and there but weight would eventually stop trains as they say.
Hope a small bit of this makes sense at least and if any part is wrong I stand to be corrected by anyone as I am no expert but believe this is how it is.