yes it is worth it, and also its depends on situation whats wrong with it.
some time repairing cost goes beyond it own worth.
Laptop has many issue, sometime there is some issue with its software and sometimes its hardware
Software problems usually take less cost to repair, complete system formatting and re-installation
its make you laptop faster, but you have to take complete backup before you format you drive, if you have more then one partition you can keep you data in secondary partition, but you have only one then you have to arrange one external drive for backup.
after taking successful backup you need one USB drive for making boot-able USB drive through that drive you will format.
Hard dist contain all your important data and you operating system, but once its formatted you data will not be back easily