Yours is a question that has been asked since the mid to late 80's when Norton came out with their first set of so called "tools". Today, there are literally dozens of programs out there that claim to double your system performance, clean up your registry, remove unneeded files, disable unnecessary start-up programs, optimize your internet settings, fix broken shortcuts, check your privacy settings, detect and delete viruses and malware, defrag you hard drive, defrag your RAM and the list goes on and on.
At the end of the day it's true that some of these programs can be useful if you really want to zero in on a particular problem and fix it. My experience has been that the more a software developer says the program will do, the less effective it becomes at doing everything it says it can. On the other hand, software that is written and designed to do only a small number of routines has been proven to be generally much more effective than the all in one programs. But if you really want to keep your system running smooth, and avoid potential problems before they pop-up, (PUN INTENDED), then you need to remember the 7 P's. Proper Prior Planning Prevents Pathetically Poor Performance!!!
After 29 years of doing this, I've found that sometimes it's quicker and easier to make sure my files are backed up properly (as they should be anyway), and do a system reload. Yes, it's true that it will take some time, but when I'm finished I have no question whatever regarding what is on my system, or if there are any lingering viruses or spyware or malware, or if the system needs to be defragmented or if the registry needs cleaning up.
When I prepare a new computer for a customer I load all of the programs they want, make sure everything is updated, email is set up, and anti-whatever is installed. I make sure there is no bloatware remaining on the system, I remove all unneeded programs from the start-up files and do a defrag to make sure all of the new files are nicely compacted and contiguous. I generally install a second hard drive with a partition for Windows System Backup, and a second partition to keep new files backed up. When this is complete, I make a clone of the primary hard drive and keep it as a back-up in my shop. If the customer is backing up their files properly and their system crashes, I can have them up and running like new in a matter of minutes with the cloned back-up.
The number of required cleaning utilities to keep such a system running at optimum speed and efficiency is zero!!! The cost for such a system is about $65.00 (for the second hard drive). Of course, if you enjoy toying around with every new registry cleaner or system optimizer that's cool. In my opinion, they are a mostly a waste of time. In general, I spend about 4 hours per day on my computer. It's an old Pentium 4 running at 3Ghz with 3GB of RAM and it's much faster than 90% of the newer computers I work on with all of the junk loaded on them.
In conclusion, back up - then backup your backup. Keep you free anti-virus up to date and your malware/spyware program at the ready and run them when you're not around. When your system starts dragging you down, slap in your backup and update and you're good as new.
Hope this helps.