I just started with a construction company and am trying to get familiar with Levelset as well. So I thought this would be a perfect opportunity to familiarize myself with Levelset and also ask for a professional answer to this question to better understand the two releases. Thank you!
The distinction between the two is an important one to understand.
An unconditional waiver is one that is effective upon execution, i.e. when the waiver is signed. If asked to execute an unconditional waiver it's important to ensure that payment has actually been received; not just a check in hand, but money deposited in your account. That's because when an unconditional waiver is signed, it is deemed an acknowledgement of receipt of payment in the amount stated on the waiver. Use these types of waivers with caution.
On the other hand, conditional waivers are the safer of the two options. They are just as effective at waiving lien rights as an unconditional waiver, with one key difference; they will not be valid or enforceable unless and until payment is received. Essentially, the waiver is conditioned on payment being made in order to be enforceable. If a conditional waiver is signed and sent over to the party, your lien rights won't be affected until the amount listed has been paid. These conditional waivers can even be sent along with an invoice or pay application to help speed up the payment process.
Note: in California (and 11 other states) there are specific statutory lien waiver forms that must be used to be valid. This helps simplify the process and ensures that there's no other additional language included that may affect other rights beyond lien rights.
Given the importance of these documents, we have a ton of resources on the subject. Here's a few articles that may prove useful: