How do tides impact your paddling?

There is barely any wind where I paddle, if we get 10kt, it is a huge day here.

We do however, have relatively big tide swings. Most days from a -0.5m low to a 5.00 high. 

Our standard session is a straight out 3.5k, straight back 3.5k (there is a tiny island to mark the turn). Unless it´s really blowing enough to creates (usable) waves moving faster than the tides, most of the time the tides end being what determine which way you go faster. 

Here in Panamá that equates to going +/-1.5 KPH faster on average with it vs against it. 

From what I understand the more popular ski'ing locations (SA-Australia) dont have as big of a tide swing, but never the less, some.

How big is the difference in speed with/against it where you paddle?

I live near São Paulo, Brazil (almost exactly on the Tropic of Capricorn). Here we also have few windy days, like you said, usually under 10kt.
Tide variation here is much smaller than in Panamá: at full moon, from a -0.2m low to a 1.5m high only.
When paddling out to sea, I really don't notice the tide. It can be felt pretty strongly in the river, though. In my last session in the river, I went up -2.5 km/h slower and went down +2.5 km/h faster than average.

5knots is a decent tidal stream but not high.

I've been on a boat in a 10knot stream and read of 13knots. 

If you are paddling at sea, you *must* pay attention to tidal flow.

From what I understand the more popular ski'ing locations (SA-Australia) dont have as big of a tide swing, but never the less, some.

How big is the difference in speed with/against it where you paddle?

Very little here in Cape Town, but the (in-) famous Agulhus current runs down the east coast of South Africa and can play a factor in races in places like East London and Port Elizabeth.  It's well known that it can be a huge advantage to move either out to sea or closer to shore during long distance races like the PE2EL Challenge.  I think the speed is around 2kt and guys keep checking their GPS to try to analyse what part of the current they're in.  

As long as paddling against the tide does not take you too long to get back, and you can get aried away paddling with the tide, the other major influence is the messy chop created by wind against tide. This can be made worse when you get complex channel junctions were tide flows run into each other

The most radical tide v wind combination I've ever paddled in was in San Francisco...  

I did a downwind on the old route of the US Surfski Champs, and near Angel Island I remember being on a run and looking down to see my GPS registering close to 0kph...  I was clearly on what was nearly a standing wave.  

That race was notorious for the currents - I recall Sean Rice winning it one year and preparing by going to see the tidal model - a massive tidal model that shows the currents in the entire bay.  He scouted out where the currents were for the time of the day for the race and that gave him an advantage.

Anyway - interesting stuff...  the magic and mystery of the ocean!