Most small businesses start tracking customers in a spreadsheet. It works for a while, until the rows multiply and the answers to who called when, and where each proposal stands, get lost.
When do you need a CRM?
If more than one person deals with the same customer, or you struggle to remember what stage a proposal is at, the order a CRM brings will prove itself quickly.
A good CRM makes the work your team already does visible; it doesn't add a new workload. The goal is to simplify the process, not complicate it.
Where to start
Starting small is best: contacts, notes and a simple sales pipeline. The rest gets added as the need arises.