Ligation: is it possible to ligate two vector backbones together - (Aug/25/2014 )

are undigested controls always necessary? especially when working with alot of plasmids?  and most of the time they just a single large band on the top never seen the three band formation as yet.

Undigested controls are mostly of use in seeing if the plasmid has been cut, or if it has been completely cut. The disappearance of the uncut plasmid band in the "cut" DNA is a good indication that your digestion worked. Otherwise, I think it is pretty useless. It also shows if you have DNA, and roughly how much, which will be a more accurate estimate than other methods, which will show genomic DNA concentrations along with the plasmid concentration.