The good news volunteering doesn’t have to affect your computer performance.
Programs such as BOINC are quite flexible and automatically detect a computer's speed and memory. As a volunteer you can set (and later change) the level of contribution in a number of ways, for example, by determining the amount of disc space, memory and CPU time to be used by the project.
You won’t strain your computer’s hardware as BOINC software can be configured to run only when the computer is not in use often as a screensaver. You can also set it to run at the lowest priority while the computer is in use. You can also limit the processor from its normal 100% to around 70% or whatever works best for you.
The idea is that you can participate in the research without it affecting your computer's performance.
If you have a powerful graphics card but are currently only working in a word processor application, the GPU will not be heavily utilised and can donate its extra power to BOINC. However, if you start playing a video game requiring a lot of graphics processing the GPU requirement will go up, and the software will automatically adjust your settings.
You can find out more on the BOINC website. You can recognise most BOINC projects by the @home suffix. Most "@home" tasks are totally independent, so it doesn't matter whether some tasks take a long time. After a "time-out" period, unfinished tasks are simply sent elsewhere to be processed.