First of all plasma is not /chaining/.
Jeez qq what have you been smoking

?
And when you see a incoming capper and you shoot a rocket in his path then it does not matter if you can chain someone down from 100->60%.
To be honest, I beg to differ. I only chain them down from 100-60% or whatever number you want if I'm NOT the only person on D. Entering the base at 60% given that they are doing an OD route, and on a small map, will probably be exiting the base at 30% ish if they are lucky to not receive any splash damage on the way out. <30% hp leaving the base is a no brainer for a chaser.
his route will be disrupted and this can be done in 50+ ping (0-50 ping is imo quite the same).
MAs are more or less the same in 0-50 ping, but chaining is certainly not, I can tell you from experience. I'm not trying to insult your intelligence or anything, but those who have 10-20 ping or less (me and st3lth) are automatically set apart from those who have 35-50+ ping. Even if we have the same "level of skill" hypothetically speaking, the <20 pinger will consistently do more damage, and quicker.
So it is more effective, and keeps you on watch for other incoming cappers. Also you can chain and then splash the stand.
Yes if you are the only one on D go for it, I tend to do that as well.