If I work on 72dpi, will the outcome(print) will be bad?

zeze88zeze  wrote I need to use the dissolve brush and 300dpi make dissolve brush too smooth so I want to work on a lower dpi.

Can you be more specific about  the effect you are trying to get?   Show us a screen shot perhaps. (Just paste it directly from the clipboard)

There are lots of was to create a dissolve type texture. Camera RAW > fx > grain is a  favourite of mine as it produces a nice texture, and you can control grain size and amount.  If you use it on a Smart Object, you can edit the affect as often as you  need to get it right.

Or Filter > Noise, or  Layer Style > Bevel & Emboss > Texture.  There are so many ways.

PPI (not dpi) is an instruction for the printer only. If the printer would indeed use that resolution, then the results will look bad.

However, in many cases the ppi setting will be ignored. The printer will simply print all the pixels on the defined paper size, which means that as long as there are enough pixels, the effective resolution will be high enough for a good print, regardless of the ppi setting.

Also note that because ppi is just an instruction, you can change this back and forth without any consequences, as long as you do not resample. If you use the 'Image Size' dialog and you uncheck the 'Resample' checkbox, then you can change between 300 ppi and 72 ppi as much as you'd like.