However, The Internet is not the only important tech for CV.
Let's take archaeology for example. Say I'm beelining archaeology (and later in the game I will beeline The Internet), and I just got a GS. I can bulb him now, and get to archaeology faster, or I can keep him, and bulb him later when I will beeline The Internet. Let's say I don't care about the maintenance, does it matter if I bulb him now or latter?
You're right, of course, that you'll get your first tech sooner if you use a GS sooner, but my point is that you'll get your
later techs
sooner if you use a GS
later. That is, if you bulb the GS to finish researching Archeology, you will get Archeology about 8 turns sooner than you would without the GS. However you will only get The Internet maybe 4 turns sooner than you would without the GS. If instead you held the GS for another two eras, by which point your science production may be double what it was when you were researching Archeology, you will get The Internet 8 turns sooner than if you hadn't had the GS at all, which is 4 turns sooner than if you used the GS back when you were researching Archeology.
That's why it's a tradeoff an an interesting game decision.
To try to make it crystal clear, I'll make up a simplified example.
From turn 192 to turn 300, you produce 100
science per turn. From turn 300 onward, you produce 300
science per turn.
It's turn 200. You've researched every tech in the Renaissance Era and none in the Industrial Era.
The two techs we care about are Archeology and The Internet.
Archeology costs 1300
.
The Internet costs 8800
. Starting from the Industrial Era, The Internet has 16 prerequisite techs. I'm not going to add up all the costs of the 17 techs, but let's estimate that it's a total of 91,000
.
Without any great scientists, it will take 13 turns to produce 1300
, so you'll get Archeology on turn 213. You'll produce 100*100
= 10,000
beakers on the 100 turns between turn 200 and 300, then you'll start producing 100
per turn after turn 300, so you'll get the Internet on turn 570:
100
* (300 - 200) + 300
* (x - 300) = 91,000
x = 570
If you bulb a great scientist on turn 200, it will produce 800
. That's 8 turns of science production in turn 200 terms, but only 2.667 turns of science production in turn 500 terms. So now you'll get Archeology on turn 205 and The Internet on turn 568.
If you bulb a great scientist on turn 562, it will produce 2400
. That's 24 turns of science production in turn 200 terms, and 8 turns of science production in turn 500 terms. You'll still get Archeology on turn 213, but now you'll get The Internet on turn 562.
So in this (contrived) example, the decision of when to bulb the GS has been reduced to two alternatives:
Use it now = getting Archeology 8 turns earlier.
Use it at the end of the game = getting the The Internet 6 turns earlier.
The correct time to use the GS will depend on game circumstances. You'll definitely want to use a GS as soon as the tech it would give you would pay serious dividends. But if the current techs you're researching don't really matter, then it will benefit you to hold it a few turns, if your science production is increasing.
for 20 turns, and if they are the top culture CIV, then that's ~20 turns longer to get influential. 
