frame ties

i know this probably has been asked a hand full of times but; what is everyone's opinion on frame ties? i have a 68 dart im doing a rotisserie restoration and my underneath will be painted the same as car! my car came with "on the side never installed" bolt on frame ties. is it worth putting on? and should i drill and bolt them on or weld them? my car isnt going to be a race car keep that in mind.