hi there need to know if it is really necessary to use spray putty

Depends what for.
I mean I wouldn't use it if all I was doing was sticking on some new body moulds now would I.

For what application?

sorry respraying the whole car i am so would i need to use spray putty on it or just spot putty

Assuming you mean 'spray-putty' in the same sense as 'high-build primer' or 'primer-filler spray', you can use it build-out shallow variations in panels. Only use it to fil wide or shallow undulations in the surface - dont use it to rescue a stuffed panel though!

Use spot-putty or an equivalent type of body filler on sharp dents or small imperfections. Be aware that it will crack off and ruin your paint job if used excessively or inappropriately. Try to repair defects in the metal if you're up to it, rather than covering it up with plastic and paint.

Stronger fibreglass body fillers can be used to fix large defects or dents, and some will approximate the strength of a steel panel when cured. You can file hard edges into it too. (Great for fixing the busted in rear-quarter corner above the tailight on an XD!)

Spraying the car in a coat of high-build primer will help in giving you a margin to flatten the panels by sanding the highs and lows. Some might argue against this? I suppose it depends on the condition of the body.

Beware that not all types of paints and primers mix - some react with each other, even when cured. Check with the guys at your auto paint store for compatability.

Also, check out your local library - they usually have books and sometime VHS/DVDs on paint and panel work. They'll have more answers than I can remember. The net is good too

Painting your car is wicked fun and you'll learn heaps. If you've not done it before, do your homework and take your time. If it stuffs up you can always do it again!

Cheers.