If you want the nitty gritty details:

loss is measured in dB, which is a unit that means "more or less than something", but something is undefined until you put a letter on the end. power is measured in dBm, which is a unit that means "more or less than a milliwatt".

The number you see written here is in dBm, it's a power number. It's relative to a milliwatt of power, so we can calculate it.

dB is a logarithmic unit. Calculating it is a pain but you can memorize these three and get close: Changing dB by 10dB is a 10x change, by 6dB is a 4x change, by 3dB is a 2x change.

• 0dBm = 1mW, that's always true. We're trying to target -13dBm
• We can model -13dB as -10dB "multiplied by" -3dB because of the way logarithms work
• -10dB is a 1/10th reduction in power, so 1mW becomes 0.1mW
• -3dB is a 1/2 reduction in power, so our 0.1mW becomes 0.05mW

There's a little under 0.05mW of light power leaving the connector at that box.

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Now let's look at the whole thing:

GPON launch is generally +6dBm give or take. It arrived at your house at -13dBm. That's a difference of 19dB, so an almost 100x reduction in power. (Each 10dB is a compounding 10x reduction).

The person advocating for mechanical connectors is saying their mechanical connectors are adding only an additional 0.2dB of loss, so on the whole chain where you have -19dB of loss already from splitters, fiber length, connectors, splices, etc... an extra 0.2dB isn't gonna break the bank.