TRIM or Wear Leveling is critical to keeping solid state hard drives healthy.  Unless a MAC computer came with an SSD from the factory, TRIM is disabled. If you upgrade a MAC with an SSD, it's important to open the Terminal application and issue the following command:

sudo trimforce enable

Solid State hard drives provide dramatic increases in both speed and reliability.  Replacing a motorized drive with an SSD means you are moving from the speed of rotating platters to the speed of electricity.  Modern SSD's rarely degrade, are less affected by impact or heat, and have become affordable.  There are various SSD form factors.  The most common form factor is 2.5" SATA, meaning it is a direct replacement for a typical laptop or desktop hard drive.  These drives can be installed in either laptop or desktop computers.  M.2 SATA drives and m.2 PCI-Express (NVMe) drives are installed in both laptops and desktops equipped with modern motherboards and the correct slot for either of these drives.  The fastest solid state drives are m.2 PCI-Express, which bypass limitations of the aging SATA bus and interface directly with the PCI-Express bus, essentially the same architecture as video cards.  However, no matter which SSD you select, it will be dramatically faster and more reliable than the best mechanical hard drive.  For best results, use SSDs with a modern operating system such as Windows 10 or Mac High Sierra (and above) to ensure the drive is maintained correctly by its internal maintenance cycle known as wear leveling or TRIM.

Slow computers are often suffering from a degraded hard drive. When a hard drive begins to wear out or degrade, sectors become weak or unreadable, causing your computer to freeze or hang while it retries the sector.  A hard drive in the early stages of failure is called a degraded drive. A degraded drive can usually be duplicated to a new drive using specialized recovery equipment.  If you suspect your drive is degraded, you should have it diagnosed for prefailure defects.

Consider cloud storage such as Google Drive, Google Photos, Google Drive Stream, Dropbox, Box, and others in an effort to safeguard your data by storing it online.  This enables you to access your data from any device, anywhere in the world by logging in with your cloud storage credentials.  Cloud storage is free or inexpensive, and your files are stored encrypted in data centers replicated all over the world. With cloud storage you are automatically syncing your folders as you work on them. Many people confuse cloud storage with cloud backup. In addition to cloud storage, files need to be backed up using services such as BackBlaze.  Backup provides versioning and static storage which is not affected by future events such as corruption, ransomware encryption, etc. Backup enables you to restore files from a point in time in the past when the file was intact.