Must admit as Danny says, pre-tied rigs made by tackle companies do make me wince, but if the need is there...
My reasons for disliking them are multiple. Biggest worry is what if I lose a fish on them due to a bad knot or hook? Who do I blame? If I have tied the rig it is my own fault, whereas if it is tackle manufacturer it may not be my fault.
Next thing, what happens if the rig is not quite right? I can shorten rigs, cut them at the swivel end, and reknot it to the mainline swivel. However I can't lengthen them. I can add an extension to the hair for the bait, an additional loop for a snowman, adding a pop-up, but often can't shorten it
I do have around 25 ready made rigs, that I have tied myself, in rig bins. I tend to design my rigs for the water I am fishing, so one rig bin contains Bromeswell rigs, one contains Nazeing rigs, and one will be Alton rigs.
The fact that I use a revolving ring on the shank means I can change hair length, lengthen or shorten it.
I do have rig tying nights at home; every hook is checked, every knot is tested. I found tying at home means I can do things at my leisure. I found tying on the bank means I may make short cuts, not check something properly.